Method of etching and polishing aluminum



Patented Nov. 3, 1953 METHOD OF ETCHING AND POLISHING ALUMINUM Virginia Terhune, East Cleveland, Ohio, assignor to The Victoreen Instrument Company, Cleveland, Ohio No Drawing. Application January 31, 1950, Serial No. 141,602

6 Claims.

This invention relates to a method of treating aluminum, and more particularly to a treatment of aluminum which will give to the metal a permanent bright polished surface, either as an end in itself or as a preparatory step in plating the aluminum.

Many treatments have been discovered, designed to remove the oxide film from aluminum as a preparatory step towards plating the piece with copper, nickel or the like. These treatments frequently required the use of an acid bath, either heated or not, or else required an electrochemical action. None of these treatments have been able to provide a permanent finish of high luster on the aluminum surface. All either required subsequent plating to provide a luster or produced a dull finish which acted as a protective coating for the aluminum against the corrosive action of the elements to which the aluminum piece was to be exposed.

I have discovered a process of treating alumlnum metal which provides a surface of high luster which is of substantial permanence. In addition to the advantages of the permanently bright surface itself, it has been discovered that aluminum treated by my new method is readily plated with copper or the like.

In the present method, the aluminum i treated in an alkaline solution in the presence of a copper salt. The solution should be at or near the boiling point. The preferred solution includes approximately 10% or less of sodium hydroxide in water and a small amount of either cuprous or cupric oxide. The precise amount of the copper oxide salt appears to be wholly unimportant to the reaction. Aluminum treated in such a mixture heated to approximately 92 degrees to 100 degree centigrade is etched to a shiny surface which is substantially permanent when subjected to ordinary atmospheric conditions.

While the mixture described is preferred, it has been discovered that the particular alkali used is not particularly important. Potassium hydroxide, trisodium phosphate, and sodium carbonate in solution of nearly the same strength as described give similar results. Nor is the particular copper salt critical. For example, copper hydroxide or copper carbonate have been used With satisfactory results. In all cases, however, the mixture must be heated to the boiling point or thereabout. Temperatures of between 92 degrees and 100 degrees centigrade have been found to be the most satisfactory.

The exact reaction of the mixture on the metal 2 is unknown to me. However, it has been discovered that the bright surface obtained from the treatment described is substantially permanent, and that the surface will receive an electrodeposition of metals such as copper or nickel with excellent results.

Having thus described my invention, I am aware that numerous and extensive departures may be made therefrom without departing from the spirit or scope of my invention.

I claim:

1. A method of treating aluminum comprising immersing the metal in a hot bath of an alkaline solution containing a dispersion of a copper bearing material, the temperature of said bath being maintained near its boiling point during the treatment.

2. A method of treating aluminum comprising the immersion of the metal in an alkaline solution containing a dispersion of a copper salt, said bath being maintained at the boiling point of the dispersion.

3. A method of treating aluminum comprising the immersion of the metal in a solution containing sodium hydroxide and a dispersion of a copper containing compound, said solution being maintained at a temperature near its boiling point.

4. The method of treating aluminum comprising the immersion of the metal in an alkaline solution containing a dispersion of copper oxide, said solution being maintained at a temperature near its boiling point.

5. The method of treating aluminum which comprises the immersion of the metal in an aqueous solution of not more than 10% sodium hydroxide and containing a dispersion of copper oxide, said solution being maintained at a temperature between 92 and degrees centigrade during the treatment.

6. The method of preparing an aluminum article for plating which comprises immersing said article in an alkaline solution containing a dispersion of a copper salt, said solution being maintained at a temperature between 92 degrees and 100 degrees centigrade during the immersion.

VIRGINIA TERHUNE.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 2,168,909 Mason Aug. 8, 1939 2,233,546 Meulendyke Mar. 4, 1941 2,318,322 Meulendyke May 4, 1943 

1. A METHOD OF TREATING ALUMINUM COMPRISING IMMERSING THE METAL IN A HOT BATH OF AN ALKALINE SOLUTION CONTAINING A DISPERSION OF A COPPER BEARING MATERIAL, THE TEMPERATURE OF SAID BATH BEING MAINTAINED NEAR ITS BOILING POINT DURING THE TREATMENT. 